I usually use a combo of moat and an earthen wall on the inside edge. Since the dwarfs throw rocks that can do slight but annoying damage to your player, crops, tamed boars, etc. the earthen wall is designed to not give them access to most targets. I also build a little slaughter tower or two where I stand above the earthen wall and shoot arrows at the gaggle of dwarfs aggroing along the moat edge.

As I haven't killed The Elder I haven't had the Earth Is Shaking troll attack yet. Apparently the club swinging troll's area of effect (AOE) can project some number of meters from where they stand so buildings too close to the perimeter can be damaged. Not sure what that AOE number is though.